NEW TEST FOR PRUSSIC ACID, ETC. 
143 
of ammonium of the excess of sulphur they contain above 
the monosulphuret ; for instance, if a mixture of prussic 
acid and ammonia be added to the pentasulphuret of am- 
monium, the solution of which is of a deep yellow colour, 
and the whole gently heated, the sulphuret of ammonium 
is soon decolourized ; and when the clear colourless liquid 
is evaporated, and the admixture of sulphuret of ammonium 
expelled, a white saline mass is obtained, which dissolves 
entirely in alcohol. The solution yields, on cooling or 
evaporation, colourless crystals of pure sulphocyanide of 
ammonium. Only a small quantity of sulphuret of ammo- 
nium is requisite to convert, in the presence of an excess of 
sulphur, unlimited quantities of cyanide of ammonium into 
sulphocyanide; because the sulphuret of ammonium, when 
reduced to the state of monosulphuret, constantly reacquires 
its power of dissolving sulphur and transferring it to the 
cyanide of ammonium. The following proportions will be 
found to be advantageous: — 2 oz. of solution of caustic am- 
monia of 0.95 spec. grav. are saturated with sulphuretted 
hydrogen gas; the hydrosulphate of ammonia thus obtained 
is mixed with 6 oz. of the same solution of ammonia, and 
to this mixture 2 oz. of flowers of sulphur are added ; and 
then the product resulting from the distillation of 6 oz. prus- 
siate of potash, 3 oz. of the hydrate of sulphuric acid, and 
18 oz. water. The mixture is digested in the water-bath 
until the sulphur is seen to be no longer altered and the 
liquid has assumed a yellow colour ; it is then heated to 
boiling, and kept at this temperature until the sulphuret of 
ammonium has been expelled, and the liquid has again be- 
come colourless. The deposited, or excess of, sulphur is 
now removed by filtration, and the liquid evaporated to 
crystallization. In this way from 3^ to 3§ oz. of dazzling 
white dry sulphocyanide of ammonium are obtained, which 
may be employed as a reagent, and for the same purposes 
as the sulphocyanide of potassium. Of the 2 oz. of sulphur 
added, \ an oz. is left undissolved. 
